Measuring responses to sound using pupillometry

ABSTRACT

A method is disclosed for testing hearing in infants based on pupil dilation response. It does not require sedation or depend on subjective judgments of human testers. Pupil dilation response to sound is measured by presenting on a display a visually engaging video containing periodic changes; presenting sounds synchronized with the periodic changes of the video; recording images from a camera directed in front of the display, where the camera is sensitive to infrared wavelengths; processing the images to measure pupil sizes; and processing the measured pupil sizes to determine, statistically, the presence of a pupil dilation response to the sounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication 62/802,607 filed Feb. 7, 2019, which is incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates generally to pupillometry systems,methods, and devices. More specifically, it relates to techniques forusing quantitative pupillometry to measure responses to sound.

BACKGROUND OF THE INVENTION

During the first 24 months of life, infants learn the sounds of theirlanguage. Hearing is therefore critical. Early identification of hearingloss has a significant impact on maintaining normal languagedevelopment, leading to the 1-3-6 guidelines of the Joint Committee onInfant Hearing (2019), which recommend that infants be screened by 1month, diagnosed by 3 months, and receive interventions by 6 months.Current diagnostic tests involve measuring the electrical activity inthe inner ear and brainstem and/or conditioning an infant to react to atest sound. However, early testing using these methods is impracticalfor the following reasons.

The measurement of electrical activity, or the auditory brainstemresponse (ABR), requires an infant to be still. Infants, especiallythose over 2 months, are often too active and must be sedated to conductan ABR. The use of sedation has significant disadvantages andcomplications. In younger infants, ABR can be measured while asleep, butsuch measurements are often interrupted by waking, resulting indiagnoses based on partial data.

ABR is not widely accessible, especially if sedation is involved.Expertise required to administer the ABR and the facilities for itsmeasurement tend to be confined to major urban centers, raisinglogistical difficulties for patients who live far from them.Consequently, significant numbers of infants miss the recommended 3month deadline for diagnosis, which is termed ‘loss-to-follow-up’.

The behavioral test, or visual reinforced audiometry (VRA), requires theconditioning of an infant to look toward the sound source or otherwisevisibly react when a sound is presented, requiring that infants be 9months or older, which is significantly older than the recommended 3month guideline. VRA is labor-intensive, requiring multiple personnelwho present the test sounds, draw and maintain an infant's attention,and infer the detection of the sound from the infant's behavior.

In VRA, whether or not the infant reacted to a presented sound isdecided subjectively. Test conclusions may thus differ when theobservers are different. Moreover, an intervention like a hearing aid orcochlear implant requires confirmation from an ABR session, reducing theutility of the VRA as a stand-alone diagnostic test.

In the standard Hughson-Westlake hearing tests, patient responses like abutton press, raised hand, or verbal response are used to assessdetection of brief test signals such as tones of different frequenciesand amplitudes. Because of its reliance on voluntary responses,Hughson-Westlake audiometry is not suitable for patients that cannotfollow instructions reliably, such as pre-lingual infants. Thus, ratherthan a standard test applicable across all ages, children are testedinstead using a battery approach, with a variety of age-specific tests.

BRIEF SUMMARY OF THE INVENTION

The present description provides a method to assess hearing, based on asound-elicited pupil dilation response (PDR). The method can identifyhearing loss in infants quickly and without need for sedation or contactwith the infant. The method can be adapted to test the discrimination ofcomplex sounds, such as those used in language, that are not typicallytested in the clinic. It can be applied to incapacitated adults andchildren of all ages, including newborns. Finally, it provides anobjective hearing test, the results of which are not influenced bysubjective judgments of testers.

A periodic animation is displayed to attract and maintain the gaze of asubject toward one or more cameras that capture images of eyes whilesounds are presented at a particular phase of the periodic animation. Acomputer processes the images to detect changes in pupil size todetermine whether the subject's pupils dilated, thus detecting asound-evoked PDR. The technique can also be used to determine whether asubject discriminated between two complex sounds, such as phonemes.

The technique is especially useful in young active children (3-24 month)as a rapid screen for hearing loss that requires no sedation orbehavioral conditioning.

In one aspect, the invention provides a method for measuring PDR tosound, the method comprising: presenting on a display to a subject avisually engaging video containing periodic changes; presenting to thesubject sounds synchronized with the periodic changes of the video;recording images from a camera directed toward the subject, where thecamera is sensitive to infrared (IR) wavelengths; processing the imagesto measure pupil sizes; and processing the measured pupil sizes todetermine, statistically, the presence of a PDR to the sounds.

Preferably, the visually engaging video is selected to have sufficientlyconstant luminance to avoid pupil contraction responses. Preferably, thevisually engaging video is selected to be sufficiently engaging suchthat a child's gaze remains focused on the animation during a majorityof a predetermined examination time. Preferably, the visually engagingvideo includes periodic patterns sufficiently repetitive to causehabituation. Preferably, the sounds are selected to cause a PDR withoutcausing a startle response. Preferably, processing the images to measurepupil sizes comprises tracking pupil location from frame to frame,extracting major and minor axes of the pupil, identifying head and eyemovements, and adjusting pupil size and shape to compensate for theidentified movements. Preferably, processing the measured pupil sizes todetermine the presence of a PDR comprises comparing pupil sizes in trialperiods with presented sounds against pupil sizes in trial periodswithout presented sounds.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a schematic diagram of a device for measuring sound-elicitedPDR according to an embodiment of the invention.

FIG. 1B is a schematic diagram illustrating an engaging periodicanimation according to an embodiment of the invention.

FIG. 1C is a schematic diagram illustrating frames of an engagingperiodic animation according to an embodiment of the invention.

FIG. 2A is a timeline illustrating synchronized animation, sound, andvideo events during intervals of a trial according to an embodiment ofthe invention.

FIG. 2B is a graph of amplitude versus time illustrating a sequence ofsound and catch trials according to an embodiment of the invention.

FIG. 3 is a graph of measured pupil diameter as a function of time for atest sound trial superimposed on that for a catch trial according to anembodiment of the invention.

FIG. 4 is an overview of the steps of a method for measuringsound-elicited PDR according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have discovered a method for detecting the PDRevoked by sounds, enabling for the first time, a simple auditory testfor nonverbal subjects. The PDR in humans is a short-latency (0.25 s)dilation of the pupil in response to novel stimuli. The PDR is acomponent of the Pavlovian orienting response, which includes covertbehaviors such as a change in heart and breathing rates and more overtbehaviors such as the turning of the head and eyes toward the stimulus.The PDR differs from dilations to changes in lighting or to exertion ofmental effort, in having a shorter latency and time-to-maximum. Notethat a PDR is evoked by salient stimuli at amplitudes ordinarilyencountered. Very loud sounds (over 90 dB SPL_(A)), by contrast, evoke aprotective response called the startle reflex, which leads to blinkingand withdrawal from the source rather than dilation and orientation.

In one embodiment, the invention provides a device for detecting the PDRto sounds, as illustrated in FIG. 1A. The device includes a display 100for displaying a video image 102 and a speaker (loudspeaker 104 orheadphones 118) for generating sounds 106. The speaker and display arecontrolled by a computer processor 108. The device also includes adigital video camera 112 that is sensitive to IR wavelengths and,preferably, a spotlight 114 generating IR light 116. Preferably, thecamera 112 is positioned above or below the center of display 100.Processor 108 controls the spotlight 114 and records video data fromcamera 112. The display 100, speaker 104, camera 112, and spotlight 114are all arranged to be oriented toward a predetermined location where ahuman subject 110 will be seated, facing toward the display 100 and inthe field of view of the camera 112. The display size and position arepreferably selected so that the displayed video image 102 fills at most20° of the subject's visual field of view. The device may be realized asa laptop or tablet computer with integrated display and camera.Alternatively, it may be realized as a desktop computer or microcomputerwith display and camera as external peripheral devices.

During an auditory examination, the device is preferably located in aquiet room with constant ambient lighting. The device is positioned infront of a seat from which a subject 110 may comfortably view thedisplay 100 while in view of the camera 112. If the subject is aninfant, the child may be placed in a car seat or a parent's lap, facingthe display 100 and video camera 112. The use of IR-sensitive camera andIR spotlight help provide good image contrast between the pupil andiris, even in subjects with dark irises.

Traditionally, gaze tracking systems that employ similar hardware haverequired subjects head to be held still via bite bars, or combinationsof chin and forehead-rests. In addition, the subject was asked to keeptheir gaze directed toward a single point, or on events of interest.However, subjects who cannot communicate or cannot understandinstructions are usually not testable, since they would be required tohave their heads restrained against their will. Further, such subjectscannot be instructed to look in a particular direction, nor can theyhold their gaze still. We discovered that an age-matched animationattracts their attention for several minutes at a time, during whichtheir heads and gaze are sufficiently still that pupil size can beaccurately computed using a combination of methods (listed below). Thus,for example, a child can be tested in a parent's lap.

During the examination of an infant, the display presents a simpleanimation having periodic changes, such as a periodic pattern of motion.The periodic animation is selected to have a substantially temporallyconstant total luminance in order to avoid a pupillary light response,i.e., a change in pupil size triggered by changes in the amount ofincident luminance. The animation is designed to be sufficientlyengaging to the child's attention that the child's gaze remains focusedon the animation during a majority of the examination time. In oneembodiment, illustrated in FIG. 1B, the animation shown on the display100 includes colorful icons or images of toys or other objects 122, 124,126 dispersed along the lower third of the monitor, which are animatedto rise and fall once every period. The duration of one period ispreferably 2-5 seconds. A different image may move during each trialperiod. At the beginning of a trial period, one image or icon 124 isanimated as described above, rises to a pre-determined height 128,remains there for a second, then descends until it returns to itsstarting position. The number of images, their rate of movement, and thenumber that move simultaneously allow us to tailor the complexity of theanimation to specific ages (Kidd et al, 2012).

As further illustrated in FIG. 1C, the three objects 122, 124, 126 arepositioned near the bottom of the screen prior to the start of eachtrial period. During 0-1 seconds of a trial, one of the objects rises upat a constant speed. During 1-2 seconds of the trial, the object remainsstill at its apex. During 2-3 seconds of the trial, the object descendsto its original position at the bottom of the screen. Finally, during3-4 seconds of the trial, all objects remain stationary at the bottom.The top row illustrates a trial in which the sun rises and falls, whilethe second row illustrates a trial in which the cloud rises and falls.This pattern of rising and falling objects is repeated each trial periodfor a randomly selected one of the three objects, except that no singleobject will rise in more than three consecutive trials.

More generally, a suitable animation for the purposes of the presentinvention is a periodic animation that engages the subject's attentionwhile not itself stimulating PDR. A sufficiently engaging animation willhold the subject's attention for a majority of the time during theexamination. Animations that are too simple (e.g., too few objects orobjects moving too slowly) or too complex (e.g., too many objects onscreen or objects moving too fast) fail to capture and retain aninfant's attention. An animation is defined as being engaging when thecomplexity and rate of change in the animation is selected between theseextremes such that the infant will spend more time looking at thedisplay than away from it. Further guidance can be found in priorresearch (Kidd et al. 2012). In the case of adult subjects, theanimation may be adapted in complexity and amount of movement.

The repeated, periodic movements in the animation cause the subject tohabituate to the visual stimulus, so that any PDR elicited by theanimation itself is quickly attenuated. If the visual input from theanimation is too complex and changing too often, the subject mayconstantly be stimulated, leading to a persistent PDR evoked by theanimation itself, drowning out the desired sound-evoked PDR. In otherwords, the animation is selected to be sufficiently engaging to retainthe subject's attention while not being so stimulating that it leads toPDR that interferes with the response to the sound. To strike thisbalance, the animation periodically repeats a pattern of movement, e.g.,an object rising on the screen, pausing at the zenith, then descendingback to the starting point, but includes variations in order to keep thecontent engaging, e.g., changes in the shape, color, location, and typeof object represented on screen.

Synchronized to the periodicity of the animation (i.e., in phase withthe animation), brief sounds (or, in some trials, periods of silence)are presented. All the while, the video camera records images of thesubject's eye(s).

FIG. 2A shows the synchronized sequence of animation (top), test-soundpresentation (middle), and video capture (bottom) events for a singletrial period 200. The trial period in this example has a duration of 4seconds, comprising four intervals of 1 second each. In the firstinterval 202 from 0-1 seconds of the trial, an object rises. In thesecond interval 204 from 1-2 seconds of the trial, the object remainsstationary at its zenith. At the beginning of this interval, a testsound 210 lasting 0.1 seconds is presented. Alternatively, if the trialis a catch trial, no sound is presented. In the third interval 206 from2-3 seconds of the trial, the object descends. In the fourth interval208 from 3-4 seconds of the trial, the object is stationary at itsnadir.

The amplitude of each test sound is typically ramped up in 5 or 10 ms toavoid spectral artifacts (e.g., clicks). These stimuli could in somecases resemble sounds used in typical hearing tests, for example, 100 msbursts of reproducible narrowband noises (approximately ⅓ octave) with acenter frequency in the range 0.5-8 kHz (e.g., 2 kHz) presented at 20-70dB SPL_(A), a range consistent with current pediatric audiologypractice.

During an examination, a sequence of trials following a similar patternare repeated, as shown in FIG. 2B. The animation in each trial followsthe same synchronized pattern as described above, except that minordetails of the animation are altered to enhance engagement of thesubject's attention. For example, variations between trials may includedifferent types or colors of objects.

In the example shown in FIG. 2B, a batch 240 of fifteen trials is shownin which twelve trials include sounds presented at four differentfrequencies and three different amplitudes per frequency. For example,test sounds 220, 224, 228 are a 20 dB 0.5 kHz pulse, a 30 dB 1 kHzpulse, and a 40 dB 2 kHz pulse. Also shown are catch trials where nosound is presented, indicated by empty pulse envelopes 222, 226, 230.When a catch trial is added, it does not replace a sound trial, butdisplaces the sound trial. In an example examination, sounds may bepresented in multiple batches, where each batch contains of 30 trials,comprising 20 sound trials (five different frequencies at 4 levels each)and 10 interspersed catch (no-sound) trials. Catch trials preferablyrepresent about ⅓ of the total trials. The presentation of differentsounds is randomized in the trials.

The sounds in different trials may have different frequencies andloudness. For example, center frequencies may be 0.5, 1, 2, 4, and 8kHz, each of which may be presented at 4 different levels of 10, 20, 30,and 40 dB SPL_(A). These auditory stimuli are presented at regularintervals in phase with the animation, e.g., at the same time that theobject reaches its highest point on the screen.

In another example examination, sounds may be presented in batches of upto 60 trials, using an ‘ascending-series order’, where sounds at thefirst frequency are presented at 20 dB, incrementing by 10 dB SPL_(A)until a response is detected. The series terminates at 70 dB, orwhatever amplitude a response is detected, and presentations of the nextfrequency commence. Paralleling standard clinical practice, if a childshows a PDR at 20 dB SPL_(A) at a given test frequency, the threshold isrecorded as 20 dB SPL_(A). On the other hand, if no significant PDR isobserved at any or all frequencies, then the amplitude is increased in10 dB steps, stepping up the ladder to a maximum of 70 dB SPL_(A) todetermine the elevated threshold. Frequencies from 0.5-4 kHz will betested in octave steps; the 2 kHz band is given priority. For infantswith elevated thresholds, where high sounds levels are required, quietersounds will be omitted in repeat ladders, shortening the session. Atmost, each frequency ‘ladder’ will comprise 6 trials from 20 to 70 dB;most ladders will be shortened on subsequent repeats. If 15 of the 60trials are set aside as catch trials, 45 trials will be available formeasurement of sound-elicited dilations, yielding multiple repeatmeasurements of each frequency-amplitude combination. Thus, eachfrequency can be tested multiple times, while still allowing for a largenumber of catch trials. If any hearing loss is detected, its severitycan be determined by accumulating data across the first batch, and ifnecessary, subsequent 4-min batches.

To compute pupil sizes objectively, we record pupil sizes during trialsin which a test sound was presented and during catch trials, which haveno sound. The catch trials are incorporated in the examination todetermine how much the pupils changed in size when no sounds arepresented. The results from these catch trials are used as a referenceagainst which pupil size obtained with a test sound is compared.

During the display of the animation and presentation of the synchronizedsounds, images of the eyes of the subject are recorded by a videocamera, where the video is precisely synchronized with the animation andsound. The video capture frame rate is preferably at least 20 to 30 fps,which is above the required frame rate for the hardware and video codecused. Using a camera that is sensitive to IR wavelengths has severaladvantages. First, since humans cannot see IR, an IR spotlight is usedto increase illumination of the subject without causing the pupils ofthe subject to constrict, whereas a visible spectrum spotlight wouldcause a pupil constriction. Second, at IR wavelengths, irises of allcolors appear gray, providing high contrast with the black pupil. Atvisual wavelengths, dark colored irises would have very low contrastwith the black pupil, making image recognition of pupil size difficult.Third, IR sensors are less likely to be impacted by unexpected changesin ambient light from fluorescent or LED lights.

For each video frame, the image is processed to recognize the pupil andcalculate its diameter. If the subject is an adult and the head can beimmobilized, image recognition of the pupil and calculation of pupilsize can be performed using commercially available techniques. In thecase of infants, where it is not practical to immobilize the head forthe duration of the examination, the infant's attention is drawn to afrontal screen showing a simple animation.

In one embodiment, calculation of pupil size where head movement maytake place involves the following steps:

-   -   1. The pupil is located within each frame, using computer vision        algorithms that locate a dark circular shape within a frame.    -   2. The pupil image shape, e.g., major and minor axes, diameter,        center of mass, and circumference are extracted.    -   3. Pupil size and location is tracked from frame to frame.        Changes in location of the center of the pupil are tracked        across frames, yielding information about translation of the        pupil on the camera sensor.    -   4. Movements orthogonal to axis of the lens, i.e., head and eye        movements away from the camera, are identified, as described in        #3 above. In addition, the ratio of major and minor axes of the        pupil indicates the direction of gaze: when the ratio is 1, both        axes are identical, and gaze is directed directly towards the        camera. When gaze is directed off-center, the diameter        orthogonal to direction of movement stays constant, while the        diameter parallel to direction of movement shrinks. Finally,        gaze direction is also determined by relative displacement        between the center of the pupil, and the reflection of the IR        spotlight from the cornea. Since the IR spotlight is located        centrally, any movement of an eye towards the midline results in        the reflection of the spotlight moving closer to the center of        the pupil and vice versa. All three of these methods are used to        determine gaze direction, and thereby to compensate for        distortions in circularity of the pupil arising from head and        eye movements. Direction and magnitude of changes in pupil shape        are determined by agreement between at least two of the three        methods.    -   5. Movements along the axis of the lens, i.e., head movement        toward or away from the camera, are identified. Such movements        are particularly important when the infant's movements are less        constrained, such as in a parent's lap. These movements result        in a change in inter-pupil distance, when both pupils are        visible, and in the change in size of other facial features,        such as iris size—not pupil size—which can be used even when        only one pupil is visible.    -   6. Computed pupil size is adjusted to compensate for eye and        head movements described in #2 to #5 above.    -   7. Detecting loss of effective imaging of the pupil due to        blinks or extremely eccentric gaze direction are identified, and        such trials are discarded.    -   8. Changes in pupil size immediately following sound        presentation are examined to determine whether or not a dilation        resulted. Dilations are determined by a consistent,        frame-to-frame increase in pupil size lasting at least 0.5        seconds. Direct size analysis is complemented by deconvolution        and correlation analysis. Consensus between these two methods is        required to determine whether a dilation was, in fact, present.

The results of a trial with a 6 month infant is shown in FIG. 3 , whichplots the average (4 trials) pupil size against time. Time is relativeto the start of the second interval of the trial, i.e., 1 second intothe trial. For test sound trials, this coincides with the onset of a 2kHz narrowband noise burst at the level of a quiet conversation, about50 dB above threshold. The pupil sizes obtained in the catch trials (11trials) are also shown. After the onset of the sound, the pupil sizeshows a clear increase, indicating dilation. In contrast, the sizeduring catch trials, which have no sound, shows no such sign ofdilation.

In one embodiment, the magnitude of PDR is quantified by computing thearea under the graph of pupil diameter with respect to time during the 2second interval starting at sound onset 1 second into the trial. Inother embodiments, the integration was over the 1.75 second intervalfrom 0.25-2 seconds after sound onset. The difference in average pupilsizes obtained in catch and sound trials is further quantified bycomputing the statistical chance that a significant dilation will occureven when there is no sound. It is relevant to note that, when theamplitude of the presented sound is lower, the PDR is smaller comparedto when the amplitude of the sound is higher. Thus, as the PDR decreasesin size for quieter presented sounds, the chances increase that ano-sound condition (catch trial) will yield a dilation that approachesthose obtained with the quiet sound. When the PDR obtained with a quietsound and in a catch trial are no longer distinguishable, we infer thatthe quiet sound was not heard, and that therefore, the subject's hearingthreshold is somewhere between the quietest sound that elicited astatistically significant dilation and the amplitude of the quiet soundthat did not yield such a dilation.

Pupil diameters at the same relative phase within each trial period areaveraged across several trial periods that have sound and separatelyacross several catch trials. If the average dilation with a sound isstatistically larger than without, we conclude that a sound was heard.

There are various ways to compare the catch trials with the test trials.These may include simple statistical tests (e.g., t-test), tests basedon signal detection theory (SDT), and methods that detect the dynamicsof a response such as deconvolution or component analysis. Objectivelyassessing the significance of any sound-induced change in pupil sizepreferably uses methods based on SDT.

The presence of a dilation during each trial period is determined aftereach sound trial by comparing results to several catch trial periods,which do not have sound. During real-time analysis, such single-trialdeterminations are used as a Yes/No determination to change from onesound frequency to another, as in FIG. 2B.

However, after the completion of a session, the ‘audiogram’,representing thresholds for the infant across all frequencies tested, isdetermined by comparing not single-trial data, but averaged data. Alltrials with a particular frequency-amplitude combination are pooled, andpupil size compared to pupil size data from pooled catch trials. Thiscomparison uses methods based on signal-detection theory, which arerelatively conservative and non-parametric, being free of assumptionsabout the type of statistical distributions that are sampled during thetesting session.

Once the video has been analyzed, results along with stimulus parameterscan be recorded, stored, transmitted, displayed, and/or otherwisecommunicated to a device operator such as a clinician.

An overview of the method is outlined in FIG. 4 . In step 400, avisually engaging video containing periodic changes is presented on adisplay. In step 402, sounds synchronized to be in phase with theperiodic changes of the video are presented. In step 404, images from anIR camera directed toward the face of a subject positioned in front ofthe display are recorded to capture images of a subject's eyes. In step406, the images are processed to measure pupil sizes represented in theimages. In step 408, the measured pupil sizes are processed todetermine, statistically, the presence of a PDR to the sound.

We also tested the effects of repeating a stimulus on the habituation ofthe PDR. Results showed that habituation can be minimized by operatingat near-threshold stimulus levels. At sound levels well above threshold,the PDR habituated and could then be recovered by changing the frequencyor amplitude of the sound. Consequently, measurement of PDR using themethods of the present invention can also be used to test stimulusdiscrimination. Given these features, the PDR may be used as anaudiometric tool or as a means of assessing auditory discrimination inthose who cannot produce a reliable voluntary response.

By replacing the presentation of alternating sounds and silence indifferent trials with the presentation of two similar phonemes (e.g.,/la/ vs /ra/) in different trials, the technique can be used to assessphoneme discrimination. Similarly, by presenting words spoken bydifferent speakers with and without noise, speech detection and speakeridentification can be assessed before and after clinical interventionssuch as speech therapy, hearing aids or cochlear implants. This is ahabituation-recovery paradigm. If a sound (habituating stimulus or HS)is repeated, the PDR elicited by later presentations is smaller thanresponses to the initial presentation. In fact, there is a significantdrop from the first to the second presentation. Further repetitioncauses the PDR to diminish even more. This is true when sounds are morethan 20 dB above threshold, and are easily audible to the subject.

Once the PDR is habituated, we can present another sound, the Recoverysound (RS). If the RS is perceived as different or novel, it will elicita PDR. If the subject cannot tell the difference between the HS and RS,the PDR will be similar to that evoked by HS.

The size of the PDR will depend on how different the RS is perceived tobe. When the habituating sound (HS) and RS differ in a simple, easilydefined physical parameter, such as intensity, the size of the PDRelicited by the RS is proportional to the difference between the twosounds.

Thus, a habituation-recovery paradigm can potentially be exploited as areporting tool to examine discrimination by habituating the PDR with oneset of stimulus parameters and testing for recovery by altering one ofthe parameters, an approach we have previously used to determineauditory discrimination thresholds in barn owls (Bala and Takahashi2000; Bala et al. 2003, 2007; Spitzer et al. 2003).

In other cases, such as speech sounds, the difference between any soundsis perceptual rather than parametric. For example, in babies raised bynative English-speaking parents, the syllables /ra/ and /la/ areperceived as different, while in babies raised by nativeJapanese-speaking parents, the two sounds are perceptuallyindistinguishable. Thus, the recovery elicited by an RS depends on howdifferent the RS is from the HS perceptually, rather than a differencethat is defined by acoustical parameters. This is especially true whenspeech sounds are involved.

The habituation-recovery paradigm has important applications, includingassessing the efficacy of interventions in infants diagnosed withhearing loss. As described above, infant hearing tests aim to meet the1-3-6 guidelines. In an ideal world, if hearing loss is diagnosed,interventions can be in place when infants are 6 months or older.Hearing aids, as well as cochlear implants, are now routinely prescribedfor infants. However, both these interventions must, as in adults, becustomized for optimal use. In adults, such optimization usesinteractive testing, allowing tuning for better speech perception. Inthe case of infants, of course, such optimization is impossible, andmust instead wait until infants are 3 to 4 years old. Thus whileinterventions are possible, these interventions cannot be assayed forefficacy.

The PDR offers a way to make such tests possible. Thehabituation-paradigm can test for optimizations of hearing aids andcochlear implants that maximize speech perception. Examples are probingphoneme discrimination, speech vs non-speech sound discrimination,which, after all, is the main goal of early intervention.Habituation-recovery can even be used to test infant's ability todiscriminate between adult-directed speech (‘adultese’) andinfant-directed speech (‘infantese’): infants have been shown to attendto the latter more than the former. This is one major lacuna in infanthearing tests, and offers a solution that currently does not exist.

The invention claimed is:
 1. A method for measuring pupil dilationresponse to sound, the method comprising: presenting on a display to asubject a visually engaging video containing an animation havingperiodic changes; presenting to the subject sounds at regular intervalsin phase with the periodic changes of the animation; recording images ofan eye of the subject from a camera directed toward eyes of the subject,where the camera is sensitive to infrared wavelengths; processing theimages to measure pupil sizes of a pupil of the eye of the subject,wherein processing the images comprises extracting major and minor axesof the pupil in each of the images and adjusting pupil size and shape tocompensate for head and eye movements; processing the measured pupilsizes to determine, statistically, the presence of a pupil dilationresponse to the sounds.
 2. The method of claim 1 wherein the visuallyengaging video is selected to have sufficiently constant luminance toavoid pupil responses to luminance changes.
 3. The method of claim 1wherein the visually engaging video is selected to be sufficientlyengaging such that a child's gaze remains focused on the animationduring a majority of a predetermined examination time.
 4. The method ofclaim 1 wherein the visually engaging video includes periodic patternssufficiently repetitive to cause habituation.
 5. The method of claim 1wherein the sounds are selected to cause a pupil dilation responsewithout causing a startle response.
 6. The method of claim 1 whereinprocessing the measured pupil sizes to determine the presence of a pupildilation response comprises comparing pupil sizes in trial periods withtest sounds against pupil sizes in trial periods without test sounds. 7.The method of claim 1 wherein processing the images to measure pupilsizes comprises tracking pupil location from frame to frame, extractingmajor and minor axes of the pupil, identifying head and eye movements,and adjusting pupil size and shape to compensate for the identified headand eye movements.